AUSTRALIAN agriculture needs a fundamental shift from a linear mining of nutrients to more efficient nutrient cycling, according to microbiologist and Soils for Life scientific adviser Walter Jehne.

The Canberra-based scientist was guest speaker at the Soils For Life Field Day at Mil Lel in the state's South East and in his speech, said it was essential for sustainable food production and the economic viability of rural communities that farmers moved from high-input agriculture which oxidises carbon from the soil to rebuilding the microbial behaviour of soil.

He said this would solubilise trace elements such as selenium and zinc now present in unavailable form.

The former CSIRO scientist said farmers who were facing a 30 per cent drop in rainfall and more variability of seasons needed to rebuild their soils to a position where they can sponge water and nutrients.

"For the last 70 years of industrial agriculture we have been oxidising the sponge, taking carbon out of our soils and collapsing our sponge so we are in a much more vulnerable state with our water," he said.

"It was all about growing bigger plants faster but that is finished and we are now into the longevity of green growth rather than the speed of growth, and plants that stay green for longer in dry times."

The present agricultural production system of using vast quantities of oil was not sustainable and becoming "prohibitively expensive", with about 10 calories of oil energy required to produce one calorie of food energy. Instead, farmers needed to move into smarter systems through cycling nutrients.

Mr Jehne said that another major benefit of improved soil was healthier food and better health.

He said the pursuit of higher yields had come at the expense of nutrient density in food, which was about a third of that in pre-World War II days.

This was leading to higher rates of obesity as people consumed more starch and sugars to meet their daily needs.

Of the world's 7.2 billion people, 3b were sub-clinically undernourished.

"We are living on N, P, K-saturated plants, with some of the other 32 essential elements needed by the body, especially some trace elements, close to zero. So we are coming down with all sorts of chronic self-induced diseases, from cancer to chronic fatigue syndrome," Mr Jehne said.

"In Australia, we are running a $145b-a-year disease industry which is growing at 8pc per annum, which is totally unsustainable and will collapse within decades."

Mr Jehne said the only way it could be addressed was through the nutritional integrity of food, and eating high-quality food for preventative health.

"Farmers will be the frontline of this. It is no longer going to be about produced raw commodities where farmers are getting five to eight cents in the dollar but premium health and premium food which can command vibrant rural businesses and regions," he said.